The present invention relates to a sheet conveying apparatus for conveying a sheet one by one from a wad of sheets.
Conventionally, the sheet conveying apparatus includes a paper feed portion, which comprises a plurality of separating portions for separating a sheet from a wad of sheets to convey the sheet one by one and a plurality of register rollers for conveying the sheet separated by the separating portions in a velocity faster than the separating portions. Each of the register roller has a wide roller width, i.e. a nip portion enough to engage the front end of the sheet to align it.
However, the conventional sheet conveying apparatus has a disadvantage that an action line of the frictional resistance force in the separating portion is shifted from that of the conveying force of the register roller, causing a couple of forces which are likely to rotate the sheet and convey it askew.
So, there has been taken such measures that straight rollers are utilized as register roller to increase the pressure-contact force and enhance the conveying force, which decreases the influence of the couple of forces. However, this causes a new disadvantage that due to the increase of the pressure-contact force, it is necessary to increase the rotational drive force and enlarge the diameter of the roller shaft, which causes enlargement of the driving apparatus and cost up as well as occurrence of sheet wrinkles.
Moreover, in the conventional sheet conveying apparatus, the conveying velocity in the separating portion is set slower than that in the register roller in order to ensure the stability of separation, which limits the conveying productivity.